More efficient and scalable thermal management systems are required in many applications ranging from electronics cooling to medical practice where localized cooling is needed as differentiated from macrocooling of a large environment.
For example, the drive for increased performance has led to smaller, faster transistors and consequently, integrated circuits with larger transistor density, higher Input/Output count, and faster clock frequency. The larger transistor density at nearly constant supply voltage and ever increasing clock frequencies has resulted in increased dynamic power dissipation. This increasing power must be dissipated by the thermal management scheme employed in the package. These trends are evidenced by the exponential increase of power density over time for state-of-the-art integrated circuits. In the latest projections of the Semiconductor Industry Association (1999), the total power dissipation is expected to push the present state-of-knowledge for thermal management. The challenge for the identification of a future thermal management technology arises from the requirement of the package to provide a robust mechanical support, a low-distortion electrical conduit for the incoming and outgoing signals, environmental protection, and thermal dissipation at low cost and high reliability.
Currently, several approaches to thermal management are used in production chip packages. For example, buoyancy-driven convective heat transfer from the heat sink to the ambient is employed for portable integrated circuit (IC) applications, while forced convection is used for high-performance IC applications. In the past, mainframe computers and supercomputers have employed complex and expensive closed-loop cooling systems using liquids. Most microprocessor and microelectronic systems have avoided closed-loop thermal management approaches due to their high cost, high power, high acoustic noise, and low reliability. These macro-scale techniques employing bulky refrigeration units are not compatible with many future microelectronic applications in high performance markets.
Efficient two-phase boiling and condensing systems capable of transferring more energy across a smaller temperature gradient can significantly help meet performance requirements for high power density and minaturized physical dimensions. Even though dropwise condensation offers heat transfer coefficients at least an order of magnitude higher than filmwise condensation, conventionally, filmwise condensation has been used in industrial condensers but not in miniaturized applications.
With the rapid advances in the area of micro-electro-mechanical systems (MEMS) in recent years, miniaturized devices are achieving higher energy effectiveness. Membranes are of particular interests in MEMS for their use as valves, pumps, and compressors in micro-fluidic devices. Membranes can use electrostatic, piezoelectric or thermal actuation to pressurize a fluid in a cavity. More recently, design concepts of miniaturized cooling systems have been proposed based on the refrigeration vapor-compression cycle (Shannon et al., 1999, and Ashraf et al., 1999). In particular, Shannon et al. (1999) have used an electrostatic diaphragm with valves to perform compression, whereas Ashraf et al. (1999) have used a centrifugal compressor. However both used conventional heat exchanger condenser and evaporator. The herein cyclic thermal management system is also based on the refrigeration vapor compression cycle, however possesses original components. In the herein system an actuated-membrane is adopted as the condensing surface as well as the ejecting device. Therefore the droplets ejected serve the dual purpose for maintaining dropwise condensation and creating a spray for highly efficient cooling.
Thus, there is a strong need for a compact, highly energy efficient device. Such a device could be connected with other similar devices to form arrays and could be incorporated in many useful devices.